The present invention relates to monitoring the cut-off function of individual cylinders or cylinder groups in internal combustion engines having multiple cylinders.
In multi-cylinder internal combustion engines, individual cylinders or cylinder groups are conventionally cut off during partial engine operation, in other words, switched between full engine operation using all cylinders, and partial engine operation using only a part of the cylinders, such as only one cylinder group of a V-engine. As a result of the cut-off, the remaining cylinders which are still operating in partial engine operation are operated with increased cylinder charge when compared to full engine operation, and thus at improved efficiency, resulting in better fuel consumption.
The cut-off may be implemented, for instance, by deactivating the gas exchange valves, e.g., those valves controlling the change of the cylinder charge. For example, the intake valve as well as the exhaust valve of the particular cylinder are closed for the duration of the deactivation to effect the cut-off.
In this context, a particular problem may arise that in those cases where full engine operation is desired, the gas exchange valves of one or more cylinders are incorrectly deactivated. Likewise, the opposite error may occur; the gas exchange valves of one or more of the cylinders to be cut off are not properly deactivated when partial engine operation is desired.
An example embodiment of the present invention makes it possible to monitor whether the valves of the cylinders capable of being shut off are properly activated during full engine operation, and whether, in partial engine operation, the valves of the cylinders to be shut off are properly deactivated.
This allows, for instance, in the case of undesirably deactivated gas exchange valves, to additionally cut off the fuel injection of the respective cylinders, so that an over-enrichment of the fuel/air mixture for the remaining cylinders may be prevented.
If no counter-measures were taken when the gas exchange valves are undesirably activated, the fuel injection of the cylinders to be cut off would be properly switched off. The undesirably active gas exchange valves cause an undesired rate of airflow through the cylinders to be cut off, which is effectively missing in the properly functioning cylinders. Since the control device calculates the fuel quantity for the properly functioning cylinders as if they were to process the entire air quantity, these cylinders are metered too much fuel, which results in deterioration in the emission behavior and in the performance of the internal combustion engine. Here, too, the amount of fuel metered to the properly working cylinders may be corrected as a counter measure.